Studies with rats and chicks have shown that low dietary levels of retinoic acid (vitamin A acid) markedly reduce the plasma and tissue concentrations of alpha-tocopherol (vitamin E) compared to animals receiving the same dietary amount of retinol (vitamin A). This effect of retinoic acid appears to be due primarily to an impairment in intestinal absorption, as shown by determining the alpha-tocopherol in lymph after radioactive alpha-tocopherol was given into the duodenum. There was no effect of dietary retinoic acid on plasma triglycerides, cholesterol or total lipids. In other studies, the utilization of vitamins A and E when given in total parenteral nutrition solutions was determined in rats. It was initially found that the plastic tubing usually used clinically for this technique completely adsorbed the solubilized vitamins A and E. Only by greatly increasing the concentration of these vitamins so that saturation of the tubing occurs has it been possible to deliver the vitamins intravenously to the animals.